1. Field of the Invention
The present invention relates to an optical movement detecting device for detecting a paper-transporting speed and/or a paper travel distance in devices such as a printer, a copying machine, and the like and also for measuring speeds of objects not having a mirror surface in a noncontact manner.
2. Description of the Related Art
A conventional optical movement detecting device, which is as shown in FIG. 11, has two distance measuring sensors 101, 102 and a processor 103.
The principle of the operation of the distance measuring sensors 101, 102 will be described below with reference to FIG. 12. Each of the distance measuring sensors 101 and 102 has an emission part 104, a lens 105 for condensing diffused light emitted from the emission part 104, a light-receiving part 107 and a lens 108 for condensing light reflected from an object 106 onto the light-receiving part 107. The light emitted by the emission part 104 is vertically incident on the object 106. Light reflected from the object 106 is condensed onto the light-receiving part 107. For the light-receiving part 107, a PSD (position sensitive device) is used.
The PSD has two output terminals. In correspondence to the position of a spot light condensed onto a light-receiving surface of the light-receiving part 107, the output ratio between the two output terminals changes.
Therefore, in the distance measuring sensor using the PSD, the output ratio between the two output terminals changes in dependence on the distance between the object to be measured and the distance measuring sensor.
More specifically, as shown in FIG. 11, when the object 106 moves in the direction shown with arrow X, the distance between the object 106 and the distance measuring sensor 101 as well as the distance measuring sensor 102 fluctuates by the amount of surface unevenness or irregularities of the object 106. As a result, the distance measuring sensors 101, 102 generate respective output signals A, B in correspondence to the amount of surface irregularities of the object 106.
FIGS. 13A and 13B show the waveforms of the output signals A and B, respectively. As is seen from these figures, in dependence on the movement speed of the object 106 in the direction shown with arrow X, the waveform of the signal B outputted from the distance measuring sensor 102 lags by Δt behind that of the signal A outputted from the distance measuring sensor 101. Based on the lag Δt, a processor 103 computes the movement speed and movement amount of the object 106.
As another background art, there is an optical movement detecting device adopting laser Doppler scheme.
The aforementioned conventional optical movement detecting device is capable of measuring the movement speed of the object 106 when it has irregularities that can be detected by the sensors 101, 102 on its surface. However it is difficult for the optical movement detecting device to measure the movement speed of the object 106 if it has a comparatively smooth surface.
The optical movement detecting device adopting the laser Doppler scheme measures the movement speed of the object by utilizing diffused light on its surface. Therefore, if the surface of the object is smooth, it is difficult to measure the movement speed. In addition, the optical movement detecting device is large in size and expensive.